The use of devices for heating and maintaining liquids at a desired temperature is known in the art. These devices typically include a container for containment of the liquid, insulation to limit the rate of heat loss from a heated liquid, a cupholder to hold the container, and a heater to heat the container. Generally, the prior art devices utilize a continuous heater which may be manually turned on or off to provide heat to the liquid in the container. Alternately, the prior art devices utilize a thermostat or a thermal-switch, such as a thermistor, to automatically switch off the heater when a predetermined temperature is reached on the surface of the container or on the surface of the heater. Such heaters include resistance-type heating elements and ceramic positive temperature coefficient ("PTC") materials. These prior art devices typically operate in an on or off mode with respect to heating the container that is independent of the amount of liquid in the container.
One prior art device attempts to compensate for the amount of liquid in the container. Such a device uses a spring-biased switch. As the amount of liquid in the container is decreased the spring-biased switch moves to an open position. When there is too little liquid weight in the container to retain the spring-biased switch in a closed position, the switch opens and the heater is switched off. Here too, the prior art device operates in an on or off mode with respect to the heater although the operation of the heater relates to the volume of liquid.
Some prior art devices rely on exposed heaters in a holder or exposed switches which activate the heater. In one prior art device, the container is place directly on an exposed heating plate located in the holder. In another prior art device, although the heater is contained within the insulation surrounding the container, the switches that activate the heater are exposed. Other prior art devices require the cup to be positioned in a specific orientation with respect to the cupholder so that an electrical connection can be made. Yet other prior art devices require the use of an external power cord to connect a source of electrical power to the cupholder.
Each of these prior art devices has certain disadvantages. Some of these devices require manual on and off operation to control the temperature of the liquid contained in the cup. Other devices must rely on thermostats or thermistors to turn off the power to the heaters. The use of exposed heaters or switches can also be a disadvantage.
The reliance on a manual operation of the heater can result in situations where the operator of such devices forgets to turn off the heater. This can result in overheating of a liquid and further result in harm to the operator. The reliance on thermostats and thermistors requires that these extra devices function properly, otherwise overheating of the liquid can occur, or the device will fail to operate at all. Also, the use of exposed heaters, or switches that activate the heater, can lead to short-circuiting of the device if the liquid is accidentally spilled on the heater or switches. The use of an exposed heater may pose a burn hazard to a user of such a device. The use of exposed heaters and/or switches also limits the type of container which may be placed in the holder. An aluminum can, for example, could short out the heater. Also, the contents of the aluminum can could be heated and overheated on an exposed heating means.
What would therefore be an advantage would be an electrically heated beverage cup and cupholder system that did not rely on manual control of the heater. It would be an advantage to have an electrically heated beverage cup and cupholder system which also did not rely on extra components such as thermostats or thermistors. It would be a further advantage to have an electrically heated beverage cup and cupholder system which provided protection against accidental spills of liquids. It would also be an advantage to have an electrically heated beverage cup and cupholder system that did not require a specific orientation of the beverage cup in the cupholder. It would be a further advantage to have a cupholder that did not require the use of an external power cord. It would be yet a further advantage to have a cupholder that allowed the placement of any properly sized container into the holder without causing problems to the operation of the electrically heated beverage cup or cupholder system.